Studies over the last many decades indicate that social network ties confer both risk and protection for health and health-relevant behavior. While studies have provided keen insights into how social networks relate to health outcomes, more theoretical work is necessary to elucidate how the structure and function of social ties act together to affect health and health-relevant behavior. Building on prior work in this area, the proposed study will examine attributes of social network ties of adolescents and their substance use behaviors, including their use of cigarettes, alcohol, and cannabis and the interdependent use of these substances. The study first proposes to test a theoretical model articulating how structural and positional attributes of adolescent friendship networks affect thei substance use behavior via two social processes or mechanisms including emotional support and peer influence. The study also examines the potential moderating role of the strength of network ties, a key dimension of friendship ties, as a theoretical pathway affecting relationships relating networks and substance use. Secondly, this study will undertake a novel approach to simulating adolescent networks forward in time, to observe the effects of perturbations to the composition of the networks, network structural and positional attributes, mechanisms under study, and substance use behaviors, ultimately to inform extant theoretical models of adolescent substance use. With three waves of data from the National Longitudinal Study of Adolescent Health, a study which was conducted using a nationally representative sample of students in grades 7-12, we utilize RSiena and statnet to estimate the study theoretical model and simulate the adolescent networks, mechanisms and substance use behaviors. The study model has potential to yield insight into the risk and protection of the network attributes and social processes under study, the overall propensity of a network as a contextual system to confer risk or protection for substance use, and information about balance points or fulcra between risk and protective processes. The proposed work has the potential to inform current theoretical understandings of how adolescent networks affect youth substance use and the more general theoretical question of how social bonds relate to health, information which may later be used to inform interventions targeting adolescent substance use. PUBLIC HEALTH RELEVANCE: The proposed study will test and simulate a model of adolescent social networks, including key structural, positional, and functional attributes, as the affect youths cigarette smoking, alcohol and cannabis use. This study has the potential to inform extant theory in the area of adolescent networks and substance use.